Month: December 2016

Part 1 – A simple transmitter, transmission line, and an “End-Fed” antenna WITHOUT a formal “Counterpoise” – We will see why common-mode current must ALWAYS flow on the coax shield.

End-Fed Antennas have been around since the good ‘ol days and were once most popular. Yet for some reason, much discord still exists regarding the “counterpoise” – what its behavior is, or if one is even needed. Not all that surprising since the term “counterpoise” doesn’t seem to have a firm definition. Hopefully, we can figure out what’s going on despite the semantics, and deal only with easy to understand basic principles.

Principles like this from basic physics:

“…charge conservation is the principle that electric charge can neither be created nor destroyed.”*

Part 3 – We place various devices at the feedpoint of an “End-Fed” antenna without a formal “Counterpoise” – We will see why the SAME common-mode current must ALWAYS flow on the coax shield just as in Part 1.

The typical “end-fed” generally has an impedance greatly different from 50 ohms, so it is rarely fed directly with coax, as losses on the transmission line will be undesirably high for lengths of coax greater than a few 10’s of meters.

Note the high loss on several bands when a 42 ft “end-fed” is directly fed with 50 ft of RG8x coax (yellow bars)* ===>

Ever wonder why successful DX-seeking stations so often use vertically polarized Verticals or Inverted-Ls on those lower bands? And why horizontal dipole-type antennas are most often seen for use on the higher shortwave bands? Even loop designs, intended for DX chasing on these lower bands, most often employ vertical polarization.

There’s good solid technical reason for this old adage:

“If you can’t get a horizontal antenna up around 3/8 wavelength or higher, then use a vertically polarized antenna.“